Field of the Invention
The present invention relates to an intake structure of an outboard motor which supplies intake air to an internal combustion engine for outboard motor.
Description of the Related Art
In general, an outboard motor is mounted on a rear section of a hull. In the rear section of the hull, waves can hit a rear surface of the outboard motor and climb upward or fall down when the ship goes rearward or rapidly decelerates. Particularly, depending on the state of water surface such as waves and swells, the shape of the hull, and the speed when going back, a large amount of water can be splashed onto the outboard motor. When the outboard motor is splashed with water, the water may enter the inside of the outboard motor and the outboard motor may fail. In an intake system of the outboard motor, a water separating function for separating water from the intake air is provided so as to correspond to being splashed with water.
Patent Document 1 has a cowling having a bottom cowl covering a bottom part of an engine and a top cowl covering an upper part of the engine. In the cowling, there is disposed a molding which partitions an air introduction chamber having a water separation structure and an engine housing chamber. Further, on the downstream of the molding, an air filter is disposed, and the air filter allows passage of only air to the engine housing chamber and blocks passage of water, salt, and garbage.
However, the molding disclosed in above-described Patent Document 1 is limited to a shape that can be disposed in the cowling since it is disposed in the cowling. That is, when the shape of the molding is changed to a shape which effectively separates air and water, it must be a shape housed within the cowling. Therefore, the shape of the molding is restricted, and thus there is a problem that it is uneasy to make a shape that effectively separates water from intake air.
Further, in general, the air inside the engine room of the outboard motor is higher in temperature than outside air due to heat radiation from the engine and a power generating device. There are outboard motors having a ventilation structure for exhausting such air inside the engine room to the outside to perform ventilation. Further, there are outboard motors having an intake passage formed independently inside the engine cover or in a cover different from the engine cover, in order to supply intake air to the engine.
The outboard motor disclosed in Patent Document 2 has an upstream intake silencer and a downstream intake silencer which are disposed outside the engine room. Air for combustion in an air intake space flows out into the upstream intake silencer via an air introduction port, and thereafter flows out to the downstream intake silencer via an air entrance port from an air lead-out port and flows out to a throttle passage via an air exit port. Further, the outboard motor of Patent Document 2 has a case in which a discharge passage part covering a transmission mechanism from above is constituted of a lower case and an upper case which is coupled air-tight to the lower case with screws, and a ventilation fan disposed in a discharge passage formed of the lower case and the upper case and sending air in a pressurized manner toward a lead-out passage.
However, although the outboard motor of above-described Patent Document 2 has the independent intake passage formed of a plurality of silencers, it is structured to be in direct contact with a ventilation space ventilated by a ventilation fan only via a partition plate such as an engine cover. Therefore, even when it has the independent intake passage, intake air temperature increases via the partition plate due to hot air in the ventilation space, where there is a concern that charging efficiency of intake decreases. Further, in order to reduce suction noise, the contact area between the intake passage and the ventilation space increases due to a silencer having a large volume, and thus the intake air temperature increases easily.
Further, generally, in an outboard motor, an intake manifold for supplying intake air to the engine is disposed at a position inside the engine cover and adjacent to the engine. Therefore, the intake manifold is heated by heat radiation of the engine and hot air in the engine cover, and the temperature of intake air in the intake manifold increases. Accordingly, there are outboard motors having a structure for cooling the intake manifold.
Patent Document 3 discloses an outboard motor provided with a water jacket for cooling intake air only in an engine side portion of an intake branch pipe constituting the intake manifold provided on one side in a traveling direction of a cylinder block. Cooling water for this water jacket for cooling intake air is supplied via a cooling water circulation path separate from a cooling water circulation path for cooling the engine. By the water jacket for cooling intake air, it is possible to prevent temperature increase of the intake manifold by heat on the engine side.
However, in the above-described cooling structure of the intake manifold disclosed in Patent Document 3, the structure becomes complicated because routing of the cooling water circulation path is necessary, and the weight of the outboard motor increases. Further, in the intake manifold, only the engine side portion is in contact with the water jacket for cooling intake air. Therefore, on an opposite side of the engine side of the intake manifold, the intake air is in contact with hot air in the engine cover and increases in temperature, where there is a concern that charging efficiency of intake air decreases.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-331666
Patent Document 2: Japanese Laid-open Patent Publication No. 2010-138858
Patent Document 3: Japanese Patent No. 3139176